Search

By measuring the actual twist angle in the twist nematic liquid crystal cell and the surface torsional angle between the rubbing direction and the liquid crystal director at the substrate boundary, a new measuring method of the surface torsional anchoring energy for pure nematic liquid crystals has been given. The relation between the surface anchoring energy and the rubbing strength was studied. The intermolecular interaction between the polymer and liquid crystal is considered very important for the alignment of liquid crystals.

In this paper a novel method is developed for measuring the twist angle and surface torsional anchoring strength in nematic liquid crystal (NLC) cells. This method is based on a technique developed from the Jones optical propagation matrix. From the measurement, the actual twist angle in NLC cell and the deviation of the LC director on the boundary of the cell from the rubbing direction of the substrate are obtained. A theoretical discussion shows that the surface torsional anchoring strength has a great influence on the value of the deviation, and hence so it can be calculated.

The investigation of the surface anchoring energy for nematic liquid crystals has always been an important branch of liquid crystal physics. By measuring the twist angle in the twist cell and the surface torsional angle between the rubbing direction and the liquid crystal director at the substrate boundary, an alternative measuring method of the surface torsional anchoring energy for pure nematic liquid crystals without chiral materials is given. The torsional anchoring energy of the interface between 4-n-pentyl-4'-cyanobiphenyl and rubbed polyimide is determined.

The surface alignment of liquid crystals is very important in preparing liquid crystal cells. The orientational effect of liquid crystal and polymide molecules on Langmuir-Blodgett(LB) films has been studied. The degree of orientation of the polyimide chain in LB films is weaker than that in strong rubbing films. The orientational effect of liquid crystals on the polyimide LB films is worse than that on the strong rubbing films. The surface azimuthal anchoring energy of liquid crystals on the polyimide LB films was measured. The intermolecular interaction between liquid crystal and polymer molecules is considered to be very important for the alignment of liquid crystals on the polymer surface.

The surface anchoring of nematic liquid crystals is an important coefficient which expresses the effect of liquid crystal alignment and the mechanism of the surface alignment. The surface azimuthal anchoring energy can be obtained by measuring the twist angle in the twist cell and the surface torsional angle between the rubbing direction and the liquid crystal director at the substrate boundary. The temperature dependence of the surface anchoring energy at 5CB-polyimide (PI) interface was studied. The surface anchoring energy decreases with increase of the temperature from ５.０×１０－5Ｊ／ｍ2 at 25.５℃ to ５.０×１０－6Ｊ／ｍ2 at 35.0℃. Meanwhile, the extrapolation length ｄe increases from 80nm at 25.5℃ to ３７０ｎｍ at ０.５℃ below Ｔc. This result clearly signifies the important role of the ordered structure of the nematic interface in determining the temperature dependence of the anchoring strength at the ５ＣＢ-PI interface.